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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Strange focus on my Sigma 35mm (art) with Dragon

I tried it on my Canon 7D and snapped a few shots and it looked better than on my Dragon.
 
Which Olpf? Could be a coatings OLPF thing. It's true that infinity can be a real bugger with stills lenses for sure. Hard to say, maybe just one of those anomalies with lens combinations.

Theorhetically, everything should work and be perfect, reality tends to get in the way of that.

But out all those things, focus shift, coatings OLPF, distance scales, etc can have an impact.
 
I have the STH OLPF. You mean there might be something with my OLPF?
 
Nope, everything Red.
 
Matt Ryan said:
are you able to rack the lenses past infinity?
Click to expand...

Yes, but that's usual for all still lenses. The critical part is that when the lens is at it's sharpest... it isn't very sharp, or rather, it has that X/Y-type bokeh I mentioned.
 
Luke Neumann said:
Chris, I noticed the same thing the other day. Something is just off with the Sigma lenses and I notice it on my 24mm 1.4 as well.
Click to expand...

I haven't resolved this yet, I have tons of editorial to do so I haven't been able to find time to try and fix it. I'm probably gonna buy cine-lenses anyway and use a PL mount so that might be a good time to see if it's the camera, the mount or lens.
 
So I did some more tests and compared my plastic 50mm with the 85mm F1.8 together with a mid range distant for them and my 35mm F1.4 Sigma.
I think I see the same type of focus-artifact. As said, it's not that they are unsharp at wide open, it's that they are vertical and horisontally unfocused when going past the focus point. It affects the CA and it makes the focused part feel "smeared" in one direction.

Here's a new test with these three. I will try and do some tests at the local rental house with another EF mount and a PL mount to see if it's the mount that's the problem.
If however this is the same using a lens like a Master Prime, then it has to be something wrong with the OLPF or sensor. What could it be if that's the case?

These are 100% crops:
Download

I would love to hear a word from Red about this. Have there been cases of the sensor upgrade creating problems with a sensor not in place or similar?
 
They way I've always found to work best for setting backfocus on the camera is to use a lens that I know is parfocal (i.e. one where the focus point doesn't shift as you zoom) of which the Tokina 11-16mm I own happens to be one. I set up a siemens star on the wall across the room, zoom in and focus the lens, then leave the focus alone, zoom out and adjust the backfocus on the camera until it is sharp. I then go back and forth a couple of times until I'm sure I've got it staying perfectly sharp at both ends of the zoom range, and every point throughout. Then I double-check that I am able to achieve infinity focus with all of my other lenses by shooting out a window.
 
This is not a backfocus issue.
 
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